Stihl 066 Service Manual PDF

The Stihl 066 is a professional-grade chainsaw known for its power and durability, widely used in forestry and demanding cutting applications. This service manual provides comprehensive technical information for maintenance, troubleshooting, and repair. It covers the MS 066 model series, including specifications, engine systems, fuel system, ignition, electrical components, clutch, chain brake, guide bar, chain, and detailed assembly/disassembly procedures. Below are key sections for safety, features, maintenance, troubleshooting, and parts information.

Features & Specifications

Key components: Two-stroke engine, electronic ignition, anti-vibration system, decompression valve, adjustable oil pump, side-access chain tensioner.

Safety Information

Always wear appropriate PPE: helmet, eye protection, hearing protection, gloves, chainsaw chaps, and sturdy boots.

1. Before servicing: Ensure engine is off, spark plug wire disconnected, and chain brake engaged.
2. Fuel handling: Use clean, fresh fuel mix (50:1 gasoline to 2-stroke oil). No smoking.
3. Chain tension: Check and adjust regularly; a loose chain can derail.
4. Working area: Keep bystanders and pets at a safe distance.

WARNING! A chainsaw is a dangerous tool. Failure to follow safety procedures can result in serious injury or death. Always refer to the operator's manual for safe operation.

Maintenance Schedule

Regular maintenance is critical for performance, safety, and longevity.

1. Daily/Before Use: Check chain tension and sharpness, check fuel and oil levels, inspect for loose fasteners, clean air filter.
2. Every 10 Hours: Clean spark arrestor screen (if equipped), check clutch drum and sprocket for wear.
3. Every 20 Hours: Replace spark plug, clean cooling fins, check anti-vibration elements.
4. Every 50 Hours: Clean fuel filter, inspect fuel lines, check carburetor adjustments.
5. Annually/Seasonally: Deep clean entire saw, check all bearings, replace worn parts, pressure test crankcase for leaks.

CAUTION! Use only genuine Stihl or approved replacement parts.

Engine Service

• Cylinder & Piston: Inspection for scoring, ring gap measurement, cylinder decompression valve service.
• Crankshaft & Bearings: Checking for play, seal replacement, connecting rod inspection.
• Crankcase: Splitting case procedure, sealant application, reassembly torque sequence.
• Muffler: Removal, cleaning of carbon deposits, spark arrestor service.
• Cooling System: Cleaning fins, checking fan wheel on flywheel.

Fuel System

Components: Fuel tank, filter, lines, carburetor (typically Walbro HD or Zama).

Carburetor Adjustment (H, L, LA screws): Initial settings: Turn H & L screws gently clockwise to stop, then back out 1 turn each. Fine-tune for optimal performance at high and low RPM. Use a tachometer for final idle (2,500-2,800 RPM) and max no-load speed (13,000 - 14,000 RPM).

Fuel Line & Filter Replacement: Symptoms of failure include hard starting, loss of power, or fuel leaks. Replace with ethanol-resistant lines if available.

Ignition System

Electronic CDI module, spark plug, stop switch, flywheel.

1. Testing Spark: Remove spark plug, connect to wire, ground plug base to cylinder, pull starter. Look for strong blue spark.
2. Air Gap: Check flywheel to ignition module gap (typically 0.3-0.4 mm / .012"-.016").
3. Module Testing: Resistance values vary by module; consult manual for specific ohms readings between terminals.
4. Stop Switch: Test for continuity; switch should break circuit when pressed.

Tip: Weak or no spark is a common cause of no-start. Check connections and grounds first.

Clutch & Chain Brake

Centrifugal clutch engages chain at ~2,800 RPM. Chain brake stops chain instantly if activated by hand or inertia.

1. Clutch Removal: Remove retaining nut, inspect shoes for wear and springs for integrity.
2. Sprocket: Check for wear (teardrop shape on drive links); replace if worn.
3. Chain Brake Band & Mechanism: Inspect for wear, cracks, or grease contamination. Test function manually.
4. Bearing: Check clutch drum bearing for smooth rotation.

WARNING! Never operate a saw with a malfunctioning chain brake. It is a critical safety device.

Guide Bar & Chain

Maintain sharp cutters, proper depth gauge height, and correct lubrication.

Bar Maintenance: Clean groove weekly, flip bar regularly for even wear, check for straightness and groove damage. Dress rails with a flat file if burred.

Chain Sharpening: Use correct round file size (.404" uses 7/32" file; 3/8" uses 13/64" file). Maintain 30° cutting angle and 10° top plate angle. File depth gauges (rakers) to proper height (0.65 mm / .025" below cutter for standard chain).

Oil System: Check oil output at bar tip. Adjust oil pump via screw (if adjustable) or replace pump if insufficient.

Troubleshooting

Reset: For electronic issues, disconnect spark plug wire for 1 minute to reset module.

Parts Diagrams

Exploded views included in manual for: Cylinder Group, Crankshaft Group, Fuel Tank Group, Clutch/Chain Brake Group, Ignition Group, Starter Group, and Outer Casing. Each part has a corresponding Stihl part number for ordering.

Common Replacement Parts: 1140 140 2005 (Piston), 1140 120 2001 (Cylinder), 1140 400 1300 (Carb Repair Kit), 0000 350 3200 (Fuel Filter), 1140 007 1005 (Ignition Module).

Torque Specifications

• Cylinder Nuts: 20 Nm (15 ft-lb)
• Spark Plug: 25 Nm (18 ft-lb)
• Clutch Nut: 40 Nm (30 ft-lb) - LEFT-HAND THREAD
• Flywheel Nut: 50 Nm (37 ft-lb)
• Muffler Bolts: 10 Nm (7.5 ft-lb)
• Guide Bar Nuts: 12 Nm (9 ft-lb)
• Crankcase Screws: 10 Nm (7.5 ft-lb)

CAUTION! Always use a torque wrench for critical fasteners. Over-tightening can strip threads; under-tightening can cause failure.

Service Support: For technical assistance or to order parts, contact an authorized Stihl servicing dealer or visit www.stihlusa.com.